Use stdbool.h on msvc

Change-Id: I8faebfc8283cd7ec178d588faaac986b8ec86900
Reviewed-on: http://review.couchbase.org/32418
Reviewed-by: Trond Norbye <trond.norbye@gmail.com>
Tested-by: Trond Norbye <trond.norbye@gmail.com>